Need to date stamp a cell if another cell contains a value

[hshayhorn]

I have an issue with a worksheet I'm using. Currently I have two sheets in my workbook. One worksheet I use to mark with an X if an employee arrives. The other sheet date and time stamps the actual time they arrive after I mark the related cell with an X. I accomplish this today with a few lines of VBA. The problem is I want to take this workbook and use it on a mobile device. Excel on a mobile device doesn't run VBA so I need to figure out another way to do this. I tried using a very basic formula =IF(Attendance!L2="","",NOW()) but every time a cell is updated every cell with the formula catches the current date and time which isn't what needs to happen. I only need the right cell updated not all cells. Does any one have any suggestions on how to do this so it will work on a mobile device? The mobile device is ideally my iPhone or iPad but could also be an android tablet too if that matters.